Preanchoring Enabled Directional Modification of Atomically Thin Membrane for High-Performance Osmotic Energy Generation

Abstract

Salinity gradient energy is an environmentally friendly energy source that possesses potential to meet the growing global energy demand. Although covalently modified nanoporous graphene membranes are prospective candidates to break the tradeoff between ion selectivity and permeability, the random reaction sites and inevitable defects during modification reduce the reaction efficiency and energy conversion performance. Here, we developed a preanchoring method to achieve directional modification near the graphene nanopores periphery. Numerical simulation revealed that the improved surface charge density around nanopores results in exceptional K + /Cl − selectivity and osmotic energy conversion performance, which agreed well with experimental results. Ionic transport measurements showed that the directionally modified graphene membranes achieved an outstanding power density of 81.6 W m −2 with an energy conversion efficiency of 35.4% under a 100-fold salinity gradient, outperforming state-of-the-art graphenebased nanoporous membranes. This work provided a facile approach for precise modification of nanoporous graphene membranes and opened up new ways for osmotic power harvesting.

Ionic Current Saturation Enabled by Cation Gating Effect in Metal–Organic-Framework Membranes

“…That offers 2D membranes more possibilities of optimizing ion transport properties by modifying the status of entrance at the membranes’ planar surfaces. For example, the charging state at the membranes’ surfaces leads to the effective rejection of co-ions and the surface conduction of counterions, contributing to the enhanced ion permeation through nanopores. − The entrance effects are also predicted to generate concentration polarization at the membrane–electrolyte interfaces, together with the nonlinear relationship between ionic current and transmembrane voltages. , Such nonlinearity makes the porous membranes interesting candidates for the creation of ionic circuits. , Nevertheless, full delivery on the promises also requires tunable ion transport under external stimuli . As exemplified in biological ion channels, their on- and off-states can be controlled by the presence of certain cations that bind on specific sites at the channels’ entrances .…”